Method and apparatus for charging partitioned capacitors

ABSTRACT

One aspect of this disclosure relates to an apparatus for providing a selective capacitance. An embodiment of the apparatus includes a first and second capacitor in a stack, and a switching circuit connected between the first and second capacitors. The switching circuit has at least two states, and is adapted to provide a first defibrillation capacitance in a first state and a second defibrillation capacitance in a second state. A switching circuit embodiment includes a field effect transistor (FET) adapted to have a source connected to the first capacitor and a drain connected to the second capacitor, a bipolar junction transistor (BJT) adapted to have an emitter connected to the source of the FET and a collector connected to a gate of the FET, a first current source connected to the collector of the BJT, and a second current source connected to a base of the BJT.

CROSS REFERENCE TO RELATED APPLICATIONS

The following commonly assigned U.S. patent application is related tothe present application and is incorporated herein by reference in itsentirety: “METHOD AND APPARATUS FOR HIGH VOLTAGE ALUMINUM CAPACITORDESIGN,” Ser. No. 11/182,707, filed on Jul. 15, 2005. The following U.S.patent applications, which are commonly assigned and filed even dateherewith, are incorporated by reference: “Method and Apparatus forSelectable Energy Storage Implantable Cardioverter Defibrillator,” Ser.No. ______ (Attorney Docket No. 279.995US1); “Method and Apparatus forPartitioned Capacitor,” Ser. No. ______ (Attorney Docket No.279.996US1).

TECHNICAL FIELD

This disclosure relates generally to electrical energy storage, and moreparticularly to methods and apparatuses including a selectable energystorage implantable cardioverter defibrillator.

BACKGROUND

Various electrical devices using capacitors are in production. Cameras,cardiac rhythm management devices and other devices use capacitors toprovide one or more pulses of electrical energy. But conventionalcapacitor designs and capacitor manufacturing problems have limited theway capacitors are used.

For example, one problem facing device manufacturers is how to providinga range of capacitances and energy levels which can be used in a device.Existing designs have yet to provide a capacitor which is adjustablewithout sacrificing packaging space, weight and manufacturingsimplicity.

Another problem facing manufacturers of implantable devices is how toprovide a device which has a capacitance and energy level which selectedbased on an impedance which is in turn based on the nature of animplantation. Existing capacitor designs are able to provide a singlecapacitance and energy level. This is especially problematic in thedefibrillation arts, which would benefit from a capacitor which providescapacitance and energy in a manner tailored for a specific use.

At the device level, there exist problems in providing an efficientelectrical device design to provide for a variety of capacitances. Newcircuit designs are needed which can provide multiple capacitances andenergy levels.

SUMMARY

The above-mentioned problems and others not expressly discussed hereinare addressed by the present subject matter and will be understood byreading and studying this specification.

Disclosed herein, among other things, is an apparatus for charging anddischarging partitioned capacitors. One embodiment of the apparatusincludes multiple capacitive elements and a switching circuit connectedbetween the capacitive elements. According to various embodiments, theswitching circuit is adapted to programmably connect a plurality of thecapacitive elements to provide a desired defibrillation capacitance. Theswitching circuit is adapted to programmably connect a plurality of thecapacitive elements to selectively charge connected elements for use ina defibrillator, according to various embodiments.

Another embodiment of the apparatus includes a first and secondcapacitor in a stack, the first and second capacitors including aplurality of substantially planar electrodes. The apparatus embodimentalso includes a switching circuit connected between the first and secondcapacitors. The switching circuit has at least two states, and isadapted to provide a first defibrillation capacitance in a first stateand a second defibrillation capacitance in a second state, according tovarious embodiments.

A further embodiment of the apparatus includes a first and secondcapacitor in a stack, the first and second capacitors including aplurality of substantially planar electrodes. The apparatus embodimentalso includes a switching circuit connected between the first and secondcapacitors. In this embodiment, the switching circuit includes a fieldeffect transistor (FET) adapted to have a source connected to the firstcapacitor and a drain connected to the second capacitor, a bipolarjunction transistor (BJT) adapted to have an emitter connected to thesource of the FET and a collector connected to a gate of the FET, afirst current source connected to the collector of the BJT, and a secondcurrent source connected to a base of the BJT. According to variousembodiments, activating the first current source turns the FET on,connecting the first and second capacitors, and activating the secondcurrent source turns the FET off, isolating the first and secondcapacitors.

One aspect of this disclosure relates to a method for making anapparatus with a variable defibrillation capacitance. According to anembodiment of the method, a first and second capacitor are formed in astack, the first and second capacitors including a plurality ofsubstantially planar electrodes, and a switching circuit is connectedbetween the first and second capacitors. The switching circuit includesa first and second state, and selecting the first state selects thefirst and second capacitor to provide a defibrillation capacitance.Selecting the second state selects the first capacitor to provide adefibrillation capacitance, according to various embodiments.

One aspect of this disclosure relates to a method for making anapparatus for charging partitioned capacitors. According to anembodiment of the method, a first and second capacitor are formed in astack, the first and second capacitors including a plurality ofsubstantially planar electrodes, and a switching circuit is connectedbetween the first and second capacitors. The switching circuit includesa field effect transistor (FET) connected between the first and secondcapacitors, a bipolar junction transistor (BJT) connected between a gateand source of the FET, a first current source connected to the gate ofthe FET, and a second current source connected to a base of the BJT.Selectively activating the first current source turns the FET on,connecting the first and second capacitors, and selectively activatingthe second current source turns the FET off, isolating the first andsecond capacitors according to various embodiments.

One aspect of this disclosure relates to a method for combining orisolating multiple capacitors within a capacitor stack. An embodiment ofthe method includes forming a first and second capacitor in a stack, thefirst and second capacitors including a plurality of substantiallyplanar electrodes. The method embodiment also includes selecting thefirst capacitor and the second capacitor by activating a firstelectrical source and selecting the first capacitor by activating asecond electrical source. According to various embodiments, the firstelectrical source and the second electrical source include a currentsource.

This Summary is an overview of some of the teachings of the presentapplication and not intended to be an exclusive or exhaustive treatmentof the present subject matter. Further details about the present subjectmatter are found in the detailed description and appended claims. Otheraspects will be apparent to persons skilled in the art upon reading andunderstanding the following detailed description and viewing thedrawings that form a part thereof, each of which are not to be taken ina limiting sense. The scope of the present invention is defined by theappended claims and their legal equivalents.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic of a power source including a first and secondcapacitor subset, according to one embodiment of the present subjectmatter.

FIG. 2 shows a schematic side view of a power source including acapacitor subset stack, according to one embodiment of the presentsubject matter.

FIG. 3A shows a schematic side view of a power source including acapacitor subset stack, according to one embodiment of the presentsubject matter.

FIG. 3B is a perspective view of the stack of FIG. 3A after the stackhas been processed according to one embodiment of the present subjectmatter.

FIG. 4A illustrates a graph representing characteristics of a capacitor,according to various embodiments of the present subject matter.

FIG. 4B illustrates a graph representing characteristics of a capacitor,according to various embodiments of the present subject matter.

FIG. 4C illustrates a graph representing characteristics of a capacitor,according to various embodiments of the present subject matter.

FIG. 5 illustrates a process for manufacturing a foil with a partiallyetched area, according to one embodiment of the present subject matter.

FIG. 6 shows a circuit for charging and discharging one or morecapacitor subsets of a multi-capacitor subset capacitor stack, accordingto one embodiment of the present subject matter.

FIG. 7 shows various capacitor wave forms based on a 40 ohm load,according to various embodiments of the present subject matter.

FIG. 8 shows various capacitor wave forms based on a 50 ohm load,according to various embodiments of the present subject matter.

FIG. 9 shows various capacitor wave forms based on a 60 ohm load,according to various embodiments of the present subject matter.

FIG. 10 shows an implantable device, according to one embodiment of thepresent subject matter.

FIG. 11A shows a wound capacitor, according to one embodiment of thepresent subject matter.

FIG. 11B shows a partially wound capacitor, according to one embodimentof the present subject matter.

DETAILED DESCRIPTION

The following detailed description of the present subject matter refersto subject matter in the accompanying drawings which show, by way ofillustration, specific aspects and embodiments in which the presentsubject matter may be practiced. These embodiments are described insufficient detail to enable those skilled in the art to practice thepresent subject matter. References to “an”, “one”, or “various”embodiments in this disclosure are not necessarily to the sameembodiment, and such references contemplate more than one embodiment.The following detailed description is demonstrative and not to be takenin a limiting sense. The scope of the present subject matter is definedby the appended claims, along with the full scope of legal equivalentsto which such claims are entitled.

The present subject matter relates to capacitors. In variousembodiments, the present subject matter includes one or more capacitorsincluding a plurality of substantially planar electrodes. In variousembodiments, these substantially planar electrodes are in a stack. Insome embodiments, the stack is plate shaped and as such, defines a flatcapacitor. Capacitors of the present subject matter include anodicelements and cathodic elements. The present subject matter additionallyincludes capacitors using electrolyte.

FIG. 1 shows a schematic of a power source including a first 102 andsecond 104 capacitor subset, according to one embodiment of the presentsubject matter. The power source 101 includes a case 110. Positionedinside the case 110, in various embodiments, is a stack 122 ofsubstantially planar capacitor electrodes. Some embodiments use foilshaped electrodes. In various embodiments, the stack 122 includescathodes and anodes. In some embodiments, case 110 is manufactured froma conductive material, such as aluminum. Stainless steel, titanium, orcombinations thereof are used in optional embodiments. These materialsare not an exhaustive or exclusive list, as other materials work withthe present subject matter. For example, in additional embodiments, thecase is manufactured using a nonconductive material, such as ceramic orplastic. The first 102 and second 104 capacitor subset store chargeindependently, in various embodiments.

In various embodiments, the case 110 includes one or more case portions.In various embodiments, the one or more case portions are connected toone another. In various embodiments, connected case portions are alsoconnected to a seal which seals the case portions to one another. Invarious embodiments, the seal is a hermetic seal. In variousembodiments, a seal can include a cured resin. In additionalembodiments, a seal can include a weld. Some embodiments of the presentsubject matter include a cured resin which resists the flow ofelectrolyte. Some of these embodiments allow for the passage of gasmolecules. Some embodiments of the present subject matter include a sealadapted to allow the passage of hydrogen atoms. Some of theseembodiments include cured epoxy resin.

Various embodiments dispose electrolyte in the case 110. In someembodiments, the electrolyte is fluidic in use. Some embodimentsincludes an electrolyte which substantially files interstices in thecase.

In various embodiments, power source 101 includes a first terminal 130and a second terminal 132 for connecting capacitor stack 122 to anoutside electrical component. In some embodiments where case 110 isconductive, first terminal 130 and second terminal 132 are feedthroughssealed to the case and electrically insulated from the case 110. Someembodiments include epoxy seals. The capacitor incorporates additionalconnection structures and methods in additional embodiments. The presentsubject matter includes, but is not limited to, additional embodimentsdisclosed on pages 12-13, 59-60, 63-82 of related and commonly assignedProvisional U.S. patent application: “Method and Apparatus for SingleHigh Voltage Aluminum Capacitor Design,” Ser. No. 60/588,905, filed onJul. 16, 2004, incorporated herein by reference.

In various embodiments, electrodes of the stack 122 are connected to thecase 110. For example, in some embodiments, cathodes 116A-N of the stackare connected to the case 110. Cathodes 116A-N can be connected with asingle mechanical connection 140, or multiple mechanical connections, invarious embodiments. In some embodiments including multiple cathodelayers which are electrically isolated from one another, the cathodesare interconnected in the case 110.

In some embodiments, the cathodes 116A-N are not connected to the case,but are instead routed out of the case through a third terminal 134. Insome embodiments, the third terminal 134 is a feedthrough sealed to case110. In additional embodiments, the third terminal is electricallyinsulated from the case 110. Additional embodiments within the presentsubject matter connect one or more anode layers to the case 110, androute the cathodes outside of the case 110 using terminals.

Capacitor stack 122 includes one or more cathode layers 116A-N, one ormore separator layers 115A-N, and one or more anode layers 114A-N, invarious embodiments. In some embodiments, these components are stackedsequentially from the top of a stack to the bottom of a stack. Theillustrated embodiment shows anode layers 114A-N which overhang cathodelayers 116A-N. It should be noted that this configuration is only one ofthe configurations possible within the scope of the present subjectmatter, and additional embodiments include configurations in which thereis no overhang. Separator layers 115A-N overhang electrodes in someembodiments of the present subject matter, and do not overhangelectrodes in additional embodiments of the present subject matter.

Additionally, in some embodiments, capacitor subcomponents are organizedinto capacitor elements 120A-N. An example element includes an anodelayer, a first separator layer, a cathode layer, and a second separatorlayers, although elements including other subcomponent configurationsare within the scope of the present subject matter.

In various embodiments, stack 122 is formed in two steps, including afirst step of stacking capacitor components into two or more elements120A-N, and a second step of stacking elements 120A-N into a stack.Various embodiment of the present subject matter include, but are notlimited to, configurations disclosed on pages 41-50 of related andcommonly assigned copending Provisional U.S. patent Publication: “Methodand Apparatus for Single High Voltage Aluminum Capacitor Design,” Ser.No. 60/588,905, filed on Jul. 16, 2004, incorporated herein byreference.

Various embodiments of the present subject matter include one or morecathode layers. In various embodiments, at least one of the cathodelayers 116A-N is metallic. Some embodiments use aluminum, tantalum,hafnium, niobium, titanium, zirconium, or combinations of these metals.Some embodiments use an aluminum substrate coated in titanium. Someembodiments including a titanium coating have an additional oxidecoating. In various embodiments, multiple cathode layers in a stack areinterconnected.

Embodiments of the present subject matter includes a third anode layerin the stack, and including a fourth terminal. A fourth terminal, invarious embodiments, is sealed to the case. Some embodiments include afeedthrough for routing the third anode through the case. A third anodemay additionally be connected to anodes of the stack 122 with a switch,as disclosed herein. Other anodes and partitions, including partitionsgreater than three, are contemplated by the present subject matter.

Interconnected layers can be interconnected using a variety of methodsand structures which include: welding the cathode layers to each other;welding the cathode layers to each other using a filler metal; andwelding an interconnection member to each layer. The presently disclosedconnections are not exhaustive or exclusive of the present subjectmatter; additional connections fall within the present scope.

Some embodiments including a titanium coated cathode material have ahigher capacitance per unit area than traditional aluminum electrolyticcapacitor cathodes. Traditional cathodes which are 98% aluminum purityor higher generally have capacitance per unit area of approximately 250uF/cm² for 30 micron thick cathode, with an oxide breakdown voltage inthe 1-3 volt range. However, a cathode as described above results in acapacitance per unit area which, in some embodiments, is as high as 1000uF/cm² or more.

Advantageously, this provides a single cathode which services an anodewithout exceeding the oxide breakdown voltage. When using a traditionalcathode to service several layers (2 or more) of anode, the cathodevoltage may rise as high as 5 or more volts, which is usually greaterthan the breakdown voltage. When this occurs, the aluminum cathodebegins to form oxide by a hydration process which extracts oxygen fromthe water present in the electrolyte. The reaction produces hydrogen asa byproduct which in turn has the effect of creating an internalpressure within the capacitor, in various embodiments. Embodimentshaving internal pressure can demonstrate an undesirable mechanical bulgein the layers of the capacitor stack, or in the case. As such, thetitanium-coated cathode described above serves as a corrective mechanismfor hydrogen generation.

Various capacitor stack embodiments use separator layers 115A-N toelectrically separate two layers. Separator layers 115A-N, in someembodiments, additionally serve as a carrier for an electrolyte. Aseparator layer 115A-N can include a single layer of kraft paper, ormultiple layers of kraft paper, in various embodiments. In someembodiments, two layers of craft paper are used to isolate a firstelectrode from a second electrode. In some of these embodiments, eachkraft paper layer is approximately 0.05 inches in thickness. In variousembodiments, the electrolyte can be any electrolyte for an electrolyticcapacitor, such as an ethylene-glycol base combined with polyphosphates,ammonium pentaborate, and/or an adipic acid solute.

Various embodiments of the present subject matter include one or moreanode layers 114A-N. In various embodiments, anodes can includealuminum, tantalum, hafnium, niobium, titanium, zirconium, andcombinations of these metals. Other compositions not listed hereinexpressly are also used as an anode.

In one embodiment, at least portions of a major surface of each anode isroughened and/or etched to increase its effective surface area. Thisoption can increase the capacitive effect of the anode on a volumetricbasis, in various embodiments. Various embodiments use tunnel-etched,core-etched, and/or perforated-core-etched structures. Variousembodiments utilize other compositions. In various embodiments, at leastone of anode layers 114A-N is a high formation voltage anode. In variousembodiments, the anodes are medium and/or low formation variations. Ananode layer 114A-N, in various embodiments, can include anode sublayers.In some embodiments, one anode layer is a multi-anode stack includingthree anode sublayers. In various embodiments, an anode layer caninclude one, two, three or more anode sublayers.

Depending on which process is used to construct the anode, varioussurfaces are coated with a dielectric. For example, in embodiments wherethe anode layers are punched from a sheet, which has previously beencoated with dielectric, only the surfaces which have not been sheared inthe punching process are coated with dielectric. Variously, if thedielectric is formed after punching, in various embodiments, allsurfaces are coated. In some embodiments, anodes are punched from alarger sheet to minimize handling defects due to handling during themanufacturing process. For example, if a larger sheet is used as astarting material from which a number of anode layers are punched,machines or operators can grasp areas of the starting material which isnot intended to form the final anode. Generally, in embodiments wherethe entire anode is not covered with dielectric, the anode is aged torestore the dielectric.

Various embodiments include a capacitor stack adapted to deliver between7.0 Joules/cubic centimeter and 8.5 Joules/cubic centimeter. Someembodiments are adapted to deliver about 7.7 Joules/cubic centimeter. Insome embodiments, the anode has a capacitance of between approximately0.70 and 0.85 microfarads per square centimeter when charged atapproximately 550 volts. In various embodiments, these ranges areavailable at a voltage of between about 410 volts to about 610 volts.

In various embodiments, the stack is disposed in a case, and linked withother components, a state which affects some of these values. Forexample, in one packaged embodiment, including a case and terminals, theenergy density available ranges from about 5.3 joules per cubiccentimeter of capacitor stack volume to about 6.3 joules per cubiccentimeter of capacitor stack volume. Some embodiments are adapted todeliver about 5.8 joules. In various embodiments, these ranges areavailable at a voltage of between about 410 volts to about 610 volts.

In various embodiments, a first capacitor stack configuration includesnine cathode layers, twenty separator layers, and twenty-eight anodelayers. One way to form such a combination would be to stack eightelements including three anode layers and one element including twoanode layers. The number of layers, and the number of elements, isselectable by a capacitor stack design and manufacturing process toachieve a desired capacitor power and thickness, in various embodiments.

In various embodiments, a second capacitor stack configuration includesnineteen cathode layers, forty separator layers, and fifty-eight anodelayers. One way to form such a combination would be to stack eighteenfirst elements, with each first element including three anode layers,one cathode layer, and two separators, with a second element includingtwo anode layers, one cathode layer, and with a third element includingtwo separators, and two anode layers. The number of layers, and thenumber of elements, is selectable by a capacitor stack design andmanufacturing process to achieve a desired capacitor power andthickness, in various embodiments. The configuration offered as anexample should not be construed as limiting, as other configurations arepossible depending on packaging and power needs of various applications.

In various embodiments of the present subject matter, a capacitorincludes 8 anode layers. In additional embodiments, a capacitor includes2 cathode layers. In some embodiments, a capacitor includes 20 anodelayers. In some embodiments, a capacitor includes 7 cathode layers.

Various embodiments of the present subject matter define two capacitivecapacitor subsets, including a first capacitor subset 102 and a secondcapacitor subset 104, by partitioning the capacitor stack 122 into afirst partition P₁ and a second partition P₂. In some embodiments of thepresent subject matter, the two capacitor subsets are defined by twogroups of interconnected anode layers. Interspersed among the two groupsof interconnected anode layers are a group of interconnected cathodelayers, in various embodiments. In various embodiments, the capacitorexhibits a first storage capacity in a first mode of operation, and asecond storage capacity in a second mode of operation. The first mode ofoperation, and the second mode of operation, in various embodiments, areselected by opening and closing a switch 106. In some embodiments, theswitch 106 is a pair of contacts which are connected mechanically. Someembodiments use solder or a jumper to interconnect the contacts. Inadditional embodiments, switch 106 is a semiconductor device which iscontrolled by software. In some embodiments, the software and thesemiconductor are integrated into the capacitor 101, and the capacitor101 is connected to electronics at terminals 111 and 112. In additionalembodiments, the terminals 130 and 132, as well as the terminal 136, areconnected to additional electronics. In these embodiments, the switch106 is integrated with those additional electronics.

In additional embodiments, switch 106 is a semiconductor device which iscontrolled by software. In some embodiments, the software and thesemiconductor are integrated into the capacitor 101, and the capacitor101 is connected to electronics at terminals 111 and 112. In additionalembodiments, the terminals 130 and 132, as well as the terminal 136, areconnected to additional electronics. In these embodiments, the switch106 is integrated with those additional electronics.

As discussed herein, the first partition and the second partition can beof different capacitances. In various embodiments, the first partitionhas a first capacitance value. In various embodiments, the partition hasa second capacitance value. In some embodiments, the first and secondcapacitance values are equivalent. In additional embodiments, the firstand second capacitance values are not equivalent. In some embodiments,one partition can store more energy than another partition. In someembodiments of the present subject matter, a first partition is sized tostore approximately three times the energy of a second partition. Asdiscussed herein, in implantable device embodiments, such a ratio ofenergy storage is useful to allow the capacitor partitions to beselected such that a first therapy energy level is available, and asecond therapy energy level is available. Having a selectable therapyenergy level allows capacitor designers and operators to adapt theimplantable medical device to the requirements of multiple situations.Such adaptability, in various embodiments, can reduce surgery time andcan improve the range of helpful treatments that are available to apatient.

In some examples within the present subject matter, a switchablecapacitor is compatible with a range of patients exhibiting a range ofimplant site impedances. In various embodiments, a care providerimplants a device into a patient. A sensor is used to establishimpedance, in various embodiments. In some embodiments, the sensor ismounted to an implanted lead which extends from the device to a shocksite, in various embodiments. A care provider, in various embodiments,measures impedance at the shock site. This impedance is patient specificand varies from patient to patient. In some embodiments, the impedanceis between approximately 40 ohms and approximately 60 ohms.

A required pulse energy level is determined, in various embodiments. Insome embodiments, a standard base level is used. In additionalembodiments, a care provider induces fibrillation, and then shocks thepatient to determine a conversion threshold. In various embodiments, theenergy required for conversion is established as a base energy value,and a generic value is added to that base value. For example, if 5joules are required for conversion, various embodiments add 10 joulesand shock the patient with a 15 joule pulse during life savingtherapies.

Capacitors within the present scope deliver a therapeutic pulse to apatient which is truncated. In various embodiments, a capacitor operatesat a tilt level. A tilt level is the level at which a certain percentageof voltage in the capacitor has dissipated. For example, a tilt level of60% represents a capacitor circuit which is designed to discharge untilthe voltage at the capacitor is 40% of what it was before the capacitorbegan to discharge. In various embodiments, switching is used totruncate capacitor dissipation. Embodiments within the present scope usea tilt voltage of from about 60% to about 80%. Some embodiments use atilt voltage which is 66%.

The pulse duration is the time required to deliver energy. In variousembodiments, the pulse duration is a function of tilt setting. The pulseduration is based, in part, on the impedance at the implant site. Invarious embodiments, design specifications limit care providers to waveforms of certain lengths, for example. If a device which is implanted inthe patient demonstrates a pulse duration which is over a specified timelimit, the device must be switched with a device which can deliver therequired amount of energy without violating the specified time limit. Assuch, a care provider would have to explant a device, and replace itwith a new device. In some embodiments, a design specification requireswave forms of a particular duration in a first region of the world inwhich a device is sold, and wave forms of a second duration in a secondregion of the world in which a device is sold. Embodiments of thepresent subject matter are suited to provide therapies in the UnitedStates and in Europe through the adjustment of switch 106. Suchadjustability, in various embodiments, provides for an improved range oftherapies care providers can administer.

A single capacitor stack including two capacitive capacitor subsets hasseveral benefits. One benefit is that two capacitor subsets can bemanufactured efficiently using manufacturing techniques used forcapacitor stacks having a single capacitive capacitor subset. Thesebenefits include the ability to weld along a single axis during theinterconnection of multiple layers. These benefits additionally includethe ability to quickly assembly a stack of fragile layers using pick andplace technology. The benefits also include a reduction in processcomplexity. By eliminating one housing, the capacitor 101 offers reducedcomplexity. Along these lines, capacitor 101 can take the place of twocapacitors in a parts inventory database. These are just some of thebenefits the present design exhibits.

FIG. 2 shows a schematic side view of a power source including acapacitor subset stack, according to one embodiment of the presentsubject matter. In various embodiments, a power source 201 includes afirst capacitor subset 202 and a second capacitor subset 204. Althoughthe capacitor subset embodiments pictured are substantially flat andplanar, other capacitor subset shapers are possible. The capacitorsubset embodiments include a stack 216 of electrodes in variousembodiments. Some embodiments include foil shaped electrodes. Thecapacitor subsets 202, 204 are disposed in a capacitor case 202.

In various embodiments, the capacitor case also houses a switch 206.Switch 206, in various embodiments, represents a pair of connectioncontacts inside the case 206 which are hardwired together duringassembly. In additional embodiments, jumpers are used. Some embodimentsinclude jumper accessible outside of a sealed implantable device. Inother embodiments, high-current switch devices are used. In someembodiments, relays controlled by circuitry outside of case 206 areused. In some embodiments, switch 206 is a semi-conductor device. Insome embodiments, switch 206 is controlled wirelessly. Some of theseembodiments use a wireless programmer to control the switch 206. Inadditional embodiments, switch 206 is controlled by computer softwareand hardware disposed in case 206. Some embodiments used feedthroughterminals 210 and 212 to program computer software and hardware whichcontrols switch 206. This list is not exhaustive or exclusive of thepresent subject matter. Other switch embodiments not expressly recitedherein additionally fall within the present scope.

Extending from the capacitor case and connected to the capacitor subsets202, 204 are feedthrough terminals, in various embodiments. For example,some embodiments include an anodic feedthrough terminal 212. Additionalembodiments include a cathodic feedthrough terminal 210. In someembodiments, the cathode terminal 210 is connected to the case 202,which is connected to a cathode of the capacitor. In some embodiments,the cathode terminal 210 is connected directly to the cathode of thecapacitor.

It should be noted that embodiments discussed herein which includeanodes and cathodes represent only a portion of the embodiments withinthe scope of the present subject matter. In additional embodiments,electrodes which are disclosed as being anodic are cathodic. Similarly,in additional embodiments, electrodes which are disclosed as beingcathodic are anodic.

FIG. 3A is a partial perspective view of a capacitor stack of one ormore anodes and cathodes, according to one embodiment of the presentsubject matter. Various embodiments include a stack 342 of one or morealternating anode layers 302 and cathode layers 303. As shown in FIG.3A, connection members 306 and 307 are overlaying and underlying eachother. In various embodiments connection members 306 and 307 have somecommonly positioned portions relative to each other and some portionswhich are exclusively positioned relative to each other. The picturedembodiment is one embodiment in which an anode connection member and acathode connection member are aligned with one another along thedirection of stacking.

For instance, proximal sections 309 of anode layers 302 are exclusivelypositioned or located. This means that at least a portion of proximalsections 309 do not overlay or underlay a portion of cathode 303.Likewise, proximal sections 308 of cathode 303 are exclusive portionsand include at least a portion not overlaying or underlaying a portionof anode layers 302. Conversely, distal sections 311 and 310 arecommonly positioned and each includes at least a portion overlaying orunderlying each another. Cut-out portions 315 and 314 are also commonlypositioned. Cut-out 319 is commonly positioned with cut-out 312 whilecut-out 313 is commonly positioned with cut-out 318.

In various stacked embodiments the edges of distal sections 311 and 310form a surface 340. In some of these embodiments, surface 340 cangenerally be described as including a first portion 340A which frontsthe proximal sections 309 of anode layers 302, a second portion 340Bwhich fronts common cut-portions 315 and 314, and third portion 340Cwhich fronts the proximal sections 308 of cathode layers 303.

In various embodiments, distal sections 311 and 310 of anode connectionmember 307 and cathode connection member 306 are fully overlaying oneanother. Fully overlaying means that there are generally no gaps alongsurface 340 of stack 342 when the anodes and cathodes are stacked. Thefully overlayed structure of stack 342 provides a complete surface 340which provides for ease of edge-welding or otherwise connectingconnection members 307 and 306 together. Other embodiments leave one ormore gaps in surface 340 when the anodes and cathodes are stacked. Forinstance, in some embodiments, one or more of distal sections 311 or 310may not reach all the way across front surface 340.

After being stacked as discussed above, at least portions of connectionmembers 307 and 306 are connected to each other. For instance, in oneembodiment, portions of distal sections 311 and 310 are connected toeach other. In one embodiment, distal sections 311 and 310 areedge-welded at least partially along surface 340. In one embodiment,distal sections 311 and 310 are only connected along portion 340A and340C of surface 340. In one embodiment, distal sections 311 and 310 aresoldered along surface 340. In some embodiments, portions of distalsections 310 and 311 are staked, swaged, laser-welded, and/or connectedby an electrically conductive adhesive. In other embodiments, portionsof proximal sections 309 are connected to each other and/or portions ofproximal sections 308 are connected to each other. In variousembodiments, insulator 370 assists in electrically isolating a firstedge weld and a second edge weld. In some embodiments, the insulator isa piece of separator paper. Other embodiments, the insulator is anotherinsulative material. In embodiments, the first edge weld defines a firstcapacitor 372, and a second edge weld defines a second capacitor 374.Additionally, some embodiments use a single edge weld to interconnectall the cathode layers 303.

After being connected, portions of connection members 307 and 306 areremoved or separated so that proximal sections 309 and 308 areelectrically isolated from each other. In some embodiments, a singleedge weld interconnects anode layers 302 of capacitor subset 372, andthen the joined anode layers 302 are excised into two or more capacitorsubsets. In one embodiment, a laser cut divides interconnected anodelayers 302 into two or more capacitor subsets. In alternate embodiments,the anode layers 302 are connected, and the cathode layers 303 areexcised into two or more capacitor subsets.

FIG. 3B is a perspective view of the stack of FIG. 3A after the stackhas been processed according to one embodiment of the present subjectmatter. FIG. 3B shows stack 342 after portions of distal sections 311and 310 have been removed from the stack, forming a separation 382between anode connection members 307, which together comprise anodeconnection section 388, and cathode connection members 306, whichtogether comprise cathode connection section 380. Separation 382 in thepresent embodiment electrically isolates section 388 from section 380.Proximal sections 308 are still coupled to each other as are proximalsections 309. In some embodiments, separation 382 is a thin slice. Insome embodiments, separation 382 is a wide cut-out. In some embodiments,an electrically insulative material is inserted in separation 382. Invarious embodiments, separation 382 is formed by laser cutting,punching, and/or tool or machine cutting. Separator 370 isolates firstcapacitor subset 372 from second capacitor subset 374.

FIGS. 4A-4C illustrate a graph representing characteristics of variousembodiments of a capacitor, according to the present subject matter. Theteachings of the present subject matter include a process for producinga capacitor which exhibits the traits illustrated by the graph. Amongthe various properties demonstrated by the graph are practicallimitations tied to various aspects of capacitor design. Overall, thegraph is useful to illustrate aspects which aid in selection anddevelopment of improved capacitors.

The graph includes a three dimensional curve representing energydelivered in joules, voltage in volts, and volume in cubic centimeters.Depending on which aspects of the graph are analyzed, various trends areapparent.

For example, FIG. 4A demonstrates embodiments in which a capacitordelivers improved energy in the range of about 465V to about 565V. Thegraph illustrates both the relationship between voltage and energydelivered, and volume and energy delivered. From reading andunderstanding the graph, it is apparent that higher voltages enablehigher energy delivered, and that a higher capacitor volume enableshigher energy delivered. The particular shape of the curves, and theenergy delivered, are, in part, functions of the surface shape of thecapacitor. For example, embodiments including capacitors with increasedsurface area due to etching, which have a dielectric formed on thesurface area without substantial reduction in the surface area, providemore energy per volumetric unit. Additionally, embodiments which haveincreased dielectric thickness enable higher voltages, which also resultin higher available energy levels. The present subject matter revealsvarying preferential ranges considering these criteria.

For example, one embodiment of the present subject matter is adapted todeliver an electrical pulse at a voltage of between approximately 490volts and approximately 540 volts. One embodiment is adapted to deliveran electrical pulse at approximately 515 volts. And additionalembodiment is adapted to deliver an electrical pulse at approximately550 volts. In some embodiments, a compromise is necessary to achieve thepreferred performance. For example, in embodiments where approximately515 volts is chosen as the operating voltage, an electrolyte which isunable to withstand higher voltages is used. In varying embodiments, anelectrolyte which is unable to operate at the peak of the voltages curveevident in the graph is chosen because of technology limitations andcost limitations. However, it is to be understood that the presentsubject matter encompasses embodiments which operate at the voltagesdemonstrated by the graph, and the examples included in these teachingsare provided solely for illustration, and are not exhaustive orexclusive.

Additionally, the present subject matter includes embodiment adapted todeliver from about 5.3 joules per cubic centimeter of capacitor stackvolume to about 6.3 joules per cubic centimeter of capacitor stackvolume. Also, the present subject matter teaches embodiments adapted todeliver from about 5.5 joules per cubic centimeter of capacitor stackvolume to about 6.1 joules per cubic centimeter of capacitor stackvolume. One embodiment is adapted to deliver about 5.8 joules per cubiccentimeter of capacitor stack.

FIG. 4B shows a top view of a graph representing various properties ofone capacitor embodiment of the present subject matter. The graphillustrates, in part, the relationship between voltage and energydelivered.

FIG. 4C includes a view of the graph which demonstrates therelationship, in part, between volume and energy delivered. In varyingembodiments, the graph teaches that volumetric energy density, measuredin joules per volt, increases when volume is minimized for a requiredenergy delivered.

Thus, by reading and understanding the information provided by thegraph, it is possible to produce a capacitor with an improved packagingdensity, including, in part, improved volumetric energy density.

FIG. 5 shows a process for making a foil with a partially etched area,according to various embodiments of the present subject matter. Invarying embodiments, the process includes depositing a curable mask ontoa foil 552. For example, in one embodiment, the mask is deposited on afoil using a computer controlled mask dispensing system. In one example,ink is deposited using an ink-jet process.

Various embodiments cure the mask onto the foil 554. Examples of curablemask include ink, and photoresist. In varying embodiments, the curablemask is cured to the foil. For example, in one embodiment, ink isdeposited on the foil, and then is baked to the foil in an oven. Baking,in some embodiments, exposes the curable mask to radiant heat energy,which can increase hardness or the curable mask, and which also candecrease the time needed for curing. In varying embodiments, the oven isadapted to cure the curable mask without affecting the foil otherwise.

In varying embodiments, the foil is etched 556, and the mask protectsthe foil from the etchant. In various embodiments, etching includescore-etching the foil, tunnel-etching the foil, perforating the foil andcombinations and permutations of these techniques. In some embodiments,perforations are formed using lasers, chemical etchants, or mechanicaldies, for example. Some embodiments tunnel-etch the foil, otherembodiments provide other known methods of providing a porous or etchedfoil. In some embodiments, a porous anode structure is constructed usingother roughening or etching techniques.

Varying examples of the process then remove the mask 558. Removing themask, in one embodiment, includes submerging the foil with mask in asolution adapted to dissolve the mask.

Some embodiments anodize the foil 560 to form a dielectric. In oneembodiment, forming a dielectric layer comprises forming a layer ofAl₂O₃ having a thickness in the range of 573 nm to 1200 nm on the anodefoil (assuming a dielectric growth rate of 1.3-1.5 nm/v). In oneembodiment, the dielectric layer is formed on the anode before thecapacitor stack is constructed.

In one embodiment, forming the dielectric layer includes applying acurrent through the anode and raising the voltage to the rated formationvoltage. In one embodiment, the formation voltage is 441 volts. In otherembodiments, the forming voltage is 450, 500, 550, 600, and 600-800volts, and other voltages ranging from approximately 441 toapproximately 800 volts or greater. The current causes a dielectricAl₂O₃ to form on the surface of the foil. Once the formation voltage isreached, the capacitor is held at that voltage until a leakage currentstabilizes at a predetermined level. By monitoring the rising voltageand/or the leakage current, the oxide formation can be estimated. Oncethe preset voltage is reached, it plateaus, in which case a current dropensues in order to balance the increasing resistance of oxide filmgrowth. The process is complete when the current drops to apre-specified value. Some embodiments combine etching and dielectricforming so that the etching and dielectric forming are donesimultaneously.

In one embodiment, method 550 results in an aluminum anode foil having aformation voltage between approximately 441 volts and approximately 600volts. In various embodiment, this includes a foil having a formationvoltage of approximately 441, approximately 450, approximately 500,approximately 550, approximately 600, and approximately 600 volts toapproximately 800 volts or greater. Varying embodiments form adielectric at approximately 600 volts to approximately 760 volts. In oneembodiment, a dielectric thickness sufficient to withstand between about653 volts and about 720 volts develops during formation. Otherembodiments withstand from about 667 volts to about 707 volts duringformation. One example is able to withstand about 687 volts duringformation.

Varied processes can be utilized to produce the aluminum foil of thepresent subject matter. For example, one process includes forming ahydrous oxide layer on an aluminum foil by immersing the foil in boilingdeionized water. The aluminum foil is also subjected to electrochemicalanodization in a bath containing an anodizing electrolyte composed of anaqueous solution of boric acid, a phosphate, and a reagent.Additionally, the anodizing electrolyte contains a phosphate. In variousembodiments, the anodizing electrolyte is at a pH of approximately 4.0to approximately 6.0. In some examples, the foil is passed through abath containing a borax solution. Borax, in various embodiments,includes a hydrated sodium borate, Na₂B₄O₇.10H₂O, and is an ore ofboron.

In varying embodiments, the foil is reanodized in the boricacid-phosphate electrolyte previously discussed. In various embodimentsof the present subject matter, the process produces a stabilized foilsuitable for oxide formation of up to approximately 760 volts.

In various embodiments, the anodizing electrolyte contains about 10grams per liter to about 120 grams per liter of boric acid andapproximately 2 to approximately 50 parts per million phosphate,preferably as phosphoric acid, and sufficient alkaline reagent to lowerthe resistivity to within approximately 1500 ohm-cm to approximately3600 ohm-cm and increase the pH from about 4.0 to about 6.0 for bestanodization efficiency and foil quality.

In some embodiments, the borax bath contains 0.001 to 0.05 moles/literof borax. Because the anodizing electrolyte is acidic, in variousembodiments, the borax bath is buffered with sodium carbonate to preventlowering of the pH by dragout of the acidic electrolyte. Additionally,in various embodiments, the borax bath is buffered to lower itsresistivity. In one example, the pH of the bath is from about 8.5 toabout 9.5, and the temperature is at least approximately 80 degreesCelsius. In varying embodiments, the sodium concentration isapproximately 0.005 to approximately 0.05M, preferably about 0.02 M. Itshould be noted that concentrations of less than approximately 0.005Mare too dilute to control properly, and concentrations aboveapproximately 0.05M increase the pH, resulting in a more reactivesolution which degrades barrier layer oxide quality.

In varying embodiments of the present subject matter, the presence of atleast approximately 2 parts per million phosphate in the acidicanodizing electrolyte is critical. For example, this presence initiatesstabilization of the foil so that solely hydrous oxide dissolves in thealkaline borax bath, without damage to the barrier layer dielectricoxide. In varying embodiments, this lowers ESR (equivalent seriesresistance) of the anodized foil.

Additionally, in various embodiments, when the foil is reanodizedfollowing the alkaline borax bath, the foil surface is alkaline andreacts electrochemically with the phosphate, which, in variousembodiments, results in the incorporation of phosphate into thedielectric oxide. In varying examples, the alkaline foil surfaceincludes an alkaline metal aluminate, and in one embodiment includes asodium aluminate. It should be noted that the amount of allowablephosphate in the anodizing electrolyte, in various embodiments, isinversely proportional to the voltage at which the foil is beinganodized. For example, in one embodiment, using greater thanapproximately 24 parts per million results in failure during oxideformation at around 650 volts. In embodiments where approximately 50parts per million of phosphate is exceeded, the electrolyte scintillatesat the foil interface, resulting in damaged, unstable foil. One benefitof the present subject matter is that an electrode is produced which cantolerate a high formation voltage without scintillation at the boundarylayer of the foil. It should be noted that anodization temperatureshould be maintained from about 85 degrees Celsius to about 95 degreesCelsius, as variance outside of these values results in a the barrierlayer oxide of lower quality, and foil corrosion.

It should be noted that these teachings should not be understood to beexhaustive or exclusive, and other methods of forming a dielectric on afoil are within the scope of the present subject matter. Additionally,it should be noted that other examples anodize the foil while the maskis in place.

In addition, varying embodiments cut the anodized foil into shapes 562,and in some examples, the foil shapes are then assembled into acapacitor 564.

According to various embodiments, an apparatus is disclosed forproviding a selective capacitance. The apparatus includes multiplecapacitive elements and a switching circuit connected between thecapacitive elements. According to various embodiments, the switchingcircuit is adapted to programmably connect a plurality of the capacitiveelements to provide a desired defibrillation capacitance. The switchingcircuit is adapted to programmably connect a plurality of the capacitiveelements to selectively charge connected elements for use in adefibrillator, according to various embodiments. The capacitive elementsare housed in an implantable medical device, according to variousembodiments.

In varying embodiments, the switching circuit is housed with thecapacitive elements. In other embodiments, the switching circuit ishoused separate from the capacitive elements. The switching circuit ishoused adjacent to the capacitive elements, in further embodiments. Theswitching circuit can be accessible from outside the implantable medicaldevice via wireless communication. Examples of wireless communicationinclude inductive telemetry and radio frequency (RF) telemetry.According to various embodiments, the switching circuit is accessiblefrom outside a human body in which the device is implanted via wirelesscommunication. The apparatus may further include a flyback capacitorcharger adapted to connect in parallel with the capacitive elements inan embodiment. According to one embodiment, the capacitive elementsinclude a first and second capacitor in a stack. As discussed, the firstand second capacitors can include a plurality of substantially planarelectrodes, in varying embodiments.

Another embodiment of the apparatus includes a first and secondcapacitor in a stack, the first and second capacitors including aplurality of substantially planar electrodes. The apparatus embodimentalso includes a switching circuit connected between the first and secondcapacitors. The switching circuit has at least two states, and isadapted to provide a first defibrillation capacitance in a first stateand a second defibrillation capacitance in a second state, according tovarious embodiments. According to varying embodiments, the stackincludes a common cathode which is shared by the first and secondcapacitor. The first defibrillation capacitance is equal to acapacitance of the first capacitor and the second defibrillationcapacitance is equal to the sum of the capacitance of the firstcapacitor and a capacitance of the second capacitor, according tovarious embodiments.

FIG. 6 shows a circuit for charging and discharging one or morecapacitor subsets of a multi-capacitor subset capacitor stack, accordingto one embodiment of the present subject matter. The circuit apparatusincludes a first capacitor 616 and second capacitor 618 in a stack, thefirst and second capacitors including a plurality of substantiallyplanar electrodes. The apparatus embodiment also includes a switchingcircuit connected between the first and second capacitors. In thisembodiment, the switching circuit includes a field effect transistor(FET, 612) adapted to have a source connected to the first capacitor anda drain connected to the second capacitor, a bipolar junction transistor(BJT, 608) adapted to have an emitter connected to the source of the FETand a collector connected to a gate of the FET, a first current source622 connected to the collector of the BJT, and a second current source620 connected to a base of the BJT. According to various embodiments,activating the first current source 622 turns the FET on, connecting thefirst and second capacitors, and activating the second current source620 turns the FET off, isolating the first and second capacitors.

The FET 612 includes a 600 volt p-channel MOSFET, according to variousembodiments. Other sizes and types of FETs may be used within the scopeof this disclosure. The FET can have a relatively high ‘on’ resistance(such as 20 ohms, in an embodiment) because the FET conducts chargingcurrent. The BJT 608 includes a small, low voltage pnp bipolar junctiontransistor, such as part number 2N2907, according to an embodiment.Other sizes and types of BJTs may be used within the scope of thisdisclosure.

According to various embodiments, the stack includes a common cathodewhich is shared by the first and second capacitor. The apparatus alsoincludes a diode 614 adapted to connect the source of the FET to thedrain of the FET. The diode 614 is adapted to conduct pulse currentduring discharge of the second capacitor, and according to variousembodiments is adapted to have 600 volt capacity. Other sizes and typesof diodes may be used within the scope of this disclosure. According tovarious embodiments, the apparatus also includes a second diode 610adapted to connect the collector of the BJT to the emitter of the BJT.The second diode 610 may include a 10 volt zener diode. Other sizes andtypes of second diodes may be used within the scope of this disclosure.According to various embodiments, the apparatus includes a flybackcapacitor charger 624 adapted to connect in parallel with the firstcapacitor.

A resistor 602 is adapted to connect the base of the BJT to the emitterof the BJT, according to various embodiments. The resistance value ofthe resistor 602 is selected to prevent the BJT from turning on due tooff-state leakage current from the second current source. Thus theresistance value of resistor 602 should be less than or equal to thevoltage drop across the base-emitter junction divided by the leakagecurrent. In various embodiments, the resistor 602 is connected inparallel with a capacitor 604, which has a value of around 10 nFaccording to an embodiment. Node 628 is adapted to connect to the supplyvoltage (Vss) and node 626 is adapted to connect to a device output,such as a defibrillator bridge, according to various embodiments.

In the depicted embodiment, both the first 616 and second 618 capacitorsare connected to the output node 626 when the first current source 622is activated during capacitor charging. In this embodiment, only thefirst capacitor is connected to the output node 626 when the secondcurrent source 620 is activated while high voltage is present on thefirst capacitor 616, which turns on BJT 608 and removes gate drive fromFET 612, turning it off.

According to various embodiments the first and second capacitors arehoused in an implantable medical device. The switching circuit may behoused with, adjacent to, or separate from the first and secondcapacitors in various embodiments. The switching circuit may beaccessible from outside the implantable medical device using acontroller 630, according to an embodiment. In one embodiment, theswitching circuit is accessible from outside a human body in which thedevice is implanted.

Another embodiment of the apparatus includes a first capacitor subset ofa multi-capacitor subset capacitor stack, a second capacitor subset of amulti-capacitor subset capacitor stack and a switching circuit connectedbetween the first and second capacitor subsets, the switching circuitadapted to charge and discharge the capacitor subsets. In thisembodiment, the switching circuit includes a high voltage field effecttransistor (FET) connected between the first and second capacitors, alow voltage bipolar junction transistor (BJT) connected between a gateand source of the FET, a first current source connected to the gate ofthe FET, and a second current source connected to a base of the BJT.According to various embodiments, activating the first current sourceturns the FET on, connecting the first and second capacitor subsets, andactivating the second current source turns the FET off, isolating thefirst and second capacitor subsets.

According to various embodiments, the first capacitor subset is adaptedto store approximately three times the energy of the second capacitorsubset. According to one embodiment, the first capacitor subset storesaround 31 Joules. The second capacitor subset stores around 10 Joules,in an embodiment.

One aspect of this disclosure relates to a method for making anapparatus with a variable defibrillation capacitance. According to anembodiment of the method, a first and second capacitor are formed in astack, the first and second capacitors including a plurality ofsubstantially planar electrodes, and a switching circuit is connectedbetween the first and second capacitors. The switching circuit includesa first and second state, and selecting the first state selects thefirst and second capacitor to provide a defibrillation capacitance.Selecting the second state selects the first capacitor to provide adefibrillation capacitance, according to various embodiments. Accordingto an embodiment, forming the first capacitor includes forming the firstcapacitor to store around 31 Joules. Forming the second capacitorincludes forming the second capacitor to store around 10 Joules,according to one embodiment.

One aspect of this disclosure relates to a method for making anapparatus for charging partitioned capacitors. According to anembodiment of the method, a first and second capacitor are formed in astack, the first and second capacitors including a plurality ofsubstantially planar electrodes, and a switching circuit is connectedbetween the first and second capacitors. The switching circuit includesa field effect transistor (FET) connected between the first and secondcapacitors, a bipolar junction transistor (BJT) connected between a gateand source of the FET, a first current source connected to the gate ofthe FET, and a second current source connected to a base of the BJT.Selectively activating the first current source turns the FET on,connecting the first and second capacitors, and selectively activatingthe second current source turns the FET off, isolating the first andsecond capacitors according to various embodiments.

According to an embodiment, connecting a FET includes connecting ap-channel MOSFET and connecting a BJT includes connecting a PNPtransistor. In various embodiments, forming a first and second capacitorin a stack includes stacking into a stack a plurality of substantiallyplanar capacitor electrodes, the stack include at least a first andsecond anode layer and a plurality of cathode layers, positioning thestack in the case, connecting the first anode layer to a firstfeedthrough disposed through the case, connecting the second anode layerto a second feedthrough disposed through the case, and connecting theplurality of cathode layers to the case. In various embodiments,connecting a switching circuit between the first and second capacitorsincludes connecting the first feedthrough, the second feedthrough, andthe case to the switching circuit.

The present subject matter includes embodiments which operate in variousways. Some applications in which the present subject matter is usedinclude a design specification which requires that a defibrillator notdeliver a therapeutic shock pulse which lasts longer than a pulseduration limit when operating at a specified tilt. The pulse durationlimit in various embodiments is 20 milliseconds, and other times areused as well. Designing a pulse which does not exceed a pulse durationlimit, but which delivers a required amount of energy, isstraightforward if the impedance of the target is known. Unfortunately,the impedance of the target is not always known. In embodiments in whicha device is implanted in a patient, target impedance is not knownbecause of anatomical variations. As such, impedance of a target is notknown until the therapeutic device is implanted. Embodiments using adevice with an active housing additionally demonstrate this phenomenon.As such, care providers often must select a capacitor for an applicationafter a device has been implanted, and site impedance has been measured.This can prolong surgery, because an initial impedance which isincorrect can require device removal and replacement during surgery.

To address the problem of unknown impedance, the present subject matterincludes embodiments which allow for selecting two or more differentcapacitances without device removal. By controlling the state of aswitch, care providers can select between the first capacitance and asecond capacitance. Varying capacitances are able to deliver requiredenergy levels at different times. Embodiments within the scope of thepresent subject matter can switch two capacitors into a parallelrelationship so that the operating voltage is the same, whilecapacitance and energy are increased. Pulse duration is adjustedaccordingly. Various embodiments include more than two capacitors.

The following table corresponds to FIGS. 7-9. FIG. 7 shows variouscapacitor wave forms based on a 40 ohm load, according to variousembodiments of the present subject matter. An example pulse durationlimit 702 is shown for the 31 J 400 μF waveform. FIG. 8 shows variouscapacitor wave forms based on a 50 ohm load, according to variousembodiments of the present subject matter. An example pulse durationlimit 802 is shown for the 31 J 400 μF waveform. FIG. 9 shows variouscapacitor wave forms based on a 60 ohm load, according to variousembodiments of the present subject matter. An example pulse durationlimit 902 is shown for the 31 J 400 μF waveform. Other impedances notlisted herein expressly also fall within the present subject matter.

Some embodiments of the present subject matter include a first capacitorsubset having a capacitance of 78 μF. In some of these embodiments, theenergy storage of the first capacitor subset is 10 joules. Some of theseembodiments include a second capacitor subset having a capacitance of232 μF. Some of these embodiments have an energy storage capacity of 31joules. Accordingly, in some of these embodiments, the first and secondcapacitor subsets, when connected in parallel, have a capacitance of 310μF. Some of these embodiments have an energy storage ability of 41joules. These examples are a capacitor subset of a larger group ofvariations possible within the scope of the present subject matter.

The table and FIGS. 7-9 show that a 400 μF capacitor charged to 393volts violates the 0.20 ms design requirement. The table also shows thata pair of capacitors switched in parallel can provide 31 J in a waveformwhich is shorter than the waveform for a 41 J capacitor. The table showshow the waveform lengths differ depending on impedance. Overall, theparallel configuration which allows an operator to use a firstcapacitor, a second capacitor or both the first capacitor and the secondcapacitor in parallel, allows for a wide range of applications with asingle device including two capacitors.

TABLE 1 Waveform Duration Waveform Duration - Stored Energy vs.Impedance (515 V) Charge Voltage 393 V 447 V 476 V 515 V 515 V 550 V 550V Capacitor Capacity 31J- 31J- 31J- 31J- 41J- 31J- 41J- 400 μF 310 μF273 μF 232 μF 310 μF 205 μF 273 μF 40Ω 16.5 ms 13.0 ms 11.0 ms  9.9 ms13.0 ms  8.9 ms 11.6 ms 50Ω 20.1 ms 15.8 ms 15.8 ms 12.1 ms 15.8 ms 10.8ms 14.0 ms 60Ω 23.7 ms 18.6 ms 18.6 ms 14.2 ms 18.6 ms 12.7 ms 16.5 ms

Various embodiments of the present subject matter include a method whichincludes implanting an implantable device, including positioning atleast a first lead proximal the heart. Various embodiments includemeasuring a system impedance at the first lead. Embodiments includecomparing the discharge time of a first capacitor operating at a firsttilt level to a threshold time. Some embodiment query if the dischargetime is higher than a threshold time. Some embodiments include, whenthis condition is met, switching the first capacitor into paralleloperation with a second capacitor of the implantable device.

The switches shown and described herein can be implemented usingsoftware, hardware, and combinations of software and hardware. As such,the term “switch” is intended to encompass software implementations,hardware implementations, and software and hardware implementations.

In various embodiments, the methods provided above are implemented as acomputer data signal embodied in a carrier wave or propagated signal,that represents a sequence of instructions which, when executed by aprocessor, cause the processor to perform the respective method. Invarious embodiments, methods provided above are implemented as a set ofinstructions contained on a computer-accessible medium capable ofdirecting a processor to perform the respective method. In variousembodiments, the medium is a magnetic medium, an electronic medium, oran optical medium.

Embodiment of Implantable Defibrillator

FIG. 10 shows one of the many applications for capacitors incorporatingone or more teachings of the present subject matter: an implantableheart monitor or apparatus 1000. As used herein, implantable heartmonitor includes any implantable device for providing therapeuticstimulus to a heart muscle. Thus, for example, the term includespacemakers, defibrillators, cardioverters, congestive heart failuredevices, and combinations and permutations thereof.

Heart monitor 1000 includes a lead system 1003, which after implantationelectrically contact strategic portions of a patient's heart. Shownschematically are portions of monitor 1000 including a monitoringcircuit 1002 for monitoring heart activity through one or more of theleads of lead system 1003, and a therapy circuit 1001 for deliveringelectrical energy through one or more of the leads to a heart. Monitor1000 also includes an energy storage component, which includes a battery1004 and incorporates at least one capacitor 1005 having one or more ofthe features of the capacitors described above.

In addition to implantable heart monitor and other cardiac rhythmmanagement devices, one or more teachings of the present subject mattercan be incorporated into cylindrical capacitors and/or capacitors usedfor photographic flash equipment. Teachings of the subject matter arepertinent to any application where high-energy, high-voltage, orspace-efficient capacitors are desirable. Moreover, one or moreteachings are applicable to batteries.

FIG. 11A shows a rolled capacitor, according to one embodiment of thepresent subject matter. In one embodiment, capacitor 1140 includes acase 1100 for carrying, enclosing, or sealing a spirally wound aluminumelectrolytic capacitor, as described below. First anode connection tab1105, second anode connection tab 1135 and cathode connection tab 1110provide electrical access to respective first anode, second anode andcathode terminals of capacitor 1140.

FIG. 11B shows a partially rolled capacitor, according to one embodimentof the present subject matter. First anode connection tab 1105physically and electrically contacts portions of a first anode 1115. Invarious embodiments, the first anode 1115 includes multiple anode layerswhich are stacked and which are in contact with one another. In variousembodiments, the first stack of anode layers includes anode layers whichare electrically interconnected. In various embodiments, these layersare strip shaped. In some embodiments, the layers are ribbon shaped.Second anode 1130 connection tab 1135 physically and electricallycontacts portions of a second anode 1130. In various embodiments, thesecond anode 1130 includes multiple anode layers which are stacked andwhich are in contact with one another. In various embodiments, thesecond stack of anode layers includes anode layers which areelectrically interconnected. In various embodiments, these layers arestrip shaped. In some embodiments, the layers are ribbon shaped. Cathodeconnection tab 1110 physically and electrically contacts portions ofcathode 1120, in various embodiments. In various embodiments, cathode1120 is strip shaped. In some embodiments, cathode 1120 is ribbonshaped. One or more separators 1125 isolate cathode 1120 from firstanode 1115 and second anode 1130.

Although specific embodiments have been illustrated and describedherein, it will be appreciated by those of ordinary skill in the artthat any arrangement which is calculated to achieve the same purpose maybe substituted for the specific embodiment shown. This application isintended to cover adaptations or variations of the present subjectmatter. It is to be understood that the above description is intended tobe illustrative, and not restrictive. Combinations of the aboveembodiments, and other embodiments will be apparent to those of skill inthe art upon reviewing the above description. The scope of the presentsubject matter should be determined with reference to the appendedclaims, along with the full scope of equivalents to which such claimsare entitled.

1. An apparatus, comprising: a plurality of capacitors; and a switchingcircuit connected between the plurality of capacitors, wherein theswitching circuit is adapted to programmably connect two or morecapacitors of the plurality of capacitors to provide a desireddefibrillation capacitance.
 2. The apparatus of claim 1, wherein theplurality of capacitors are housed in an implantable medical device. 3.The apparatus of claim 2, wherein the switching circuit is housed withthe plurality of capacitors.
 4. The apparatus of claim 2, wherein theswitching circuit is housed separate from the plurality of capacitors.5. The apparatus of claim 4, wherein the switching circuit is housedadjacent to the plurality of capacitors.
 6. The apparatus of claim 2,wherein the switching circuit is accessible from outside the implantablemedical device via wireless communication.
 7. The apparatus of claim 2,wherein the switching circuit is accessible from outside a human body inwhich the device is implanted via wireless communication.
 8. Anapparatus, comprising: a plurality of capacitors; and a switchingcircuit connected between the plurality of capacitors, wherein theswitching circuit is adapted to programmably connect two or morecapacitors of the plurality of capacitors to selectively chargeconnected elements for use in a defibrillator.
 9. The apparatus of claim8, further comprising: a flyback capacitor charger adapted to connect inparallel with the two or more capacitors of the plurality of capacitors.10. The apparatus of claim 8, wherein the plurality of capacitorsincludes a first and second capacitor in a stack.
 11. The apparatus ofclaim 10, wherein the first and second capacitors include a plurality ofsubstantially planar electrodes.
 12. An apparatus, comprising: a firstand second capacitor in a stack, the first and second capacitorsincluding a plurality of substantially planar electrodes; and aswitching circuit connected between the first and second capacitors, theswitching circuit having at least two states, wherein the switchingcircuit is adapted to provide a first defibrillation capacitance in afirst state and a second defibrillation capacitance in a second state.13. The apparatus of claim 12, wherein the stack includes a commoncathode which is shared by the first and second capacitor.
 14. Theapparatus of claim 12, wherein the first defibrillation capacitance isequal to a capacitance of the first capacitor and the seconddefibrillation capacitance is equal to the sum of the capacitance of thefirst capacitor and a capacitance of the second capacitor.
 15. Anapparatus, comprising: a first and second capacitor in a stack, thefirst and second capacitors including a plurality of substantiallyplanar electrodes; a switching circuit connected between the first andsecond capacitors, the switching circuit including: a field effecttransistor (FET) adapted to have a source connected to the firstcapacitor and a drain connected to the second capacitor; a bipolarjunction transistor (BJT) adapted to have an emitter connected to thesource of the FET and a collector connected to a gate of the FET; afirst current source connected to the collector of the BJT, whereinactivating the first current source turns the FET on, connecting thefirst and second capacitors; and a second current source connected to abase of the BJT, wherein activating the second current source turns theFET off, isolating the first and second capacitors.
 16. The apparatus ofclaim 15, wherein the stack includes a common cathode which is shared bythe first and second capacitor.
 17. The apparatus of claim 15, furthercomprising: a diode adapted to connect the source of the FET to thedrain of the FET, the diode adapted to conduct during discharge of thesecond capacitor.
 18. The apparatus of claim 15, further comprising: adiode adapted to connect the collector of the BJT to the emitter of theBJT.
 19. The apparatus of claim 15, further comprising: a resistoradapted to connect the base of the BJT to the emitter of the BJT,wherein a resistance value of the resistor is selected to prevent theBJT from turning on due to off-state leakage current from the secondcurrent source.
 20. A method, comprising: forming a first and secondcapacitor in a stack, the first and second capacitors including aplurality of substantially planar electrodes; forming a switchingcircuit between the first and second capacitors, the switching circuithaving a first and second state; selecting the first capacitor and thesecond capacitor to provide a defibrillation capacitance by selectingthe first state of the switching circuit; and selecting the firstcapacitor to provide the defibrillation capacitance by selecting thesecond state of the switching circuit.
 21. The method of claim 20,wherein forming the first capacitor includes forming the first capacitorto store around 31 Joules.
 22. The method of claim 20, wherein formingthe second capacitor includes forming the second capacitor to storearound 10 Joules.
 23. A method, comprising: forming a first and secondcapacitor in a stack, the first and second capacitors including aplurality of substantially planar electrodes; connecting a switchingcircuit between the first and second capacitors, wherein connecting theswitching circuit includes: connecting a field effect transistor (FET)between the first and second capacitors; connecting a bipolar junctiontransistor (BJT) between a gate and source of the FET; connecting afirst current source to the gate of the FET; connecting a second currentsource to a base of the BJT; selectively activating the first currentsource to turn the FET on, connecting the first and second capacitors;and selectively activating the second current source to turn the FEToff, isolating the first and second capacitors.
 24. The method of claim23, wherein connecting a FET includes connecting a p-channel MOSFET. 25.The method of claim 23, wherein connecting a BJT includes connecting aPNP transistor.
 26. The method of claim 23, wherein forming a first andsecond capacitor in a stack includes: stacking into the stack aplurality of substantially planar capacitor electrodes, the stackinclude at least a first and second anode layer and a plurality ofcathode layers; positioning the stack in the case; connecting the firstanode layer to a first feedthrough disposed through the case; connectingthe second anode layer to a second feedthrough disposed through thecase; and connecting the plurality of cathode layers to the case. 27.The method of claim 26, wherein connecting a switching circuit betweenthe first and second capacitors includes connecting the firstfeedthrough, the second feedthrough, and the case to the switchingcircuit.